Bixbyite with Quartz on Topaz
Manganese Iron Oxide (Mn,FE)2O3
Crystal System: Isometric
- Bixbyite is a rare mineral that occurs as opaque, black, cubic crystals with a metallic to submetallic
luster. The crystals are often modified by trapezohedrons and sometimes occur as penetration twins.
It occurs in cavities in rhyolite and is associated with garnet, topaz, beryl and hematite. Bixbyite
is a minor ore of manganese.
Silicon Dioxide, SiO2
Crystal System: Hexagonal
- Quartz is by far the most abundant of the polymorphic forms of silica and the most widespread and abundant
mineral of the earth's crust. It occurs in igneous, metamorphic and sedimentary rocks as well as hydrothermal
veins, metasomatic and hot spring deposits.
Hydrous Aluminum Silicate Al2SiO4(F,OH)2
Crystal System: Orthorhombic
- Topaz is a widely distributed mineral that is associated with granites, pegmatites, rhyolites and also occurs
in greisen and pneumatolytic bodies. It occurs as prismatic crystals, often with vertical striations on the
faces, and is quite variable in color. White to pale yellow color is most common, and yellow to sherry colors
are most often associated with topaz. However, topaz also occurs in pale blue to green colors, with natural
pink to red specimens being the rarest. Many specimens have been found that exhibit cavities of various sizes
which are filled with gaseous liquids or crystals of ilmenite, hematite, and rutile. Very large pieces of
topaz have been found, some weighing upwards of 600 pounds.
- Topaz is used as gem material by jewelers and lapidary hobbyists. The natural color of topaz may be altered by
heating it in the presence of various gases, an old process sometimes referred to as "pinking." Some topaz
specimens exhibit sensitivity to light, and loose color if exposed to strong sources or for long periods of
time. In gem circles, the name "topaz" is rather generically used to describe yellow stones, including quartz
Rocks from Martin Friedlander's Collection
Index of Specimen Images
Table of Contents